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|
# -----------------------------------------------------------------------------
# calc.py
#
# A simple calculator with variables. This is from O'Reilly's
# "Lex and Yacc", p. 63.
#
# This example uses unicode strings for tokens, docstrings, and input.
# -----------------------------------------------------------------------------
import sys
sys.path.insert(0,"../..")
tokens = (
'NAME','NUMBER',
'PLUS','MINUS','TIMES','DIVIDE','EQUALS',
'LPAREN','RPAREN',
)
# Tokens
t_PLUS = ur'\+'
t_MINUS = ur'-'
t_TIMES = ur'\*'
t_DIVIDE = ur'/'
t_EQUALS = ur'='
t_LPAREN = ur'\('
t_RPAREN = ur'\)'
t_NAME = ur'[a-zA-Z_][a-zA-Z0-9_]*'
def t_NUMBER(t):
ur'\d+'
try:
t.value = int(t.value)
except ValueError:
print "Integer value too large", t.value
t.value = 0
return t
t_ignore = u" \t"
def t_newline(t):
ur'\n+'
t.lexer.lineno += t.value.count("\n")
def t_error(t):
print "Illegal character '%s'" % t.value[0]
t.lexer.skip(1)
# Build the lexer
import ply.lex as lex
lex.lex()
# Parsing rules
precedence = (
('left','PLUS','MINUS'),
('left','TIMES','DIVIDE'),
('right','UMINUS'),
)
# dictionary of names
names = { }
def p_statement_assign(p):
'statement : NAME EQUALS expression'
names[p[1]] = p[3]
def p_statement_expr(p):
'statement : expression'
print p[1]
def p_expression_binop(p):
'''expression : expression PLUS expression
| expression MINUS expression
| expression TIMES expression
| expression DIVIDE expression'''
if p[2] == u'+' : p[0] = p[1] + p[3]
elif p[2] == u'-': p[0] = p[1] - p[3]
elif p[2] == u'*': p[0] = p[1] * p[3]
elif p[2] == u'/': p[0] = p[1] / p[3]
def p_expression_uminus(p):
'expression : MINUS expression %prec UMINUS'
p[0] = -p[2]
def p_expression_group(p):
'expression : LPAREN expression RPAREN'
p[0] = p[2]
def p_expression_number(p):
'expression : NUMBER'
p[0] = p[1]
def p_expression_name(p):
'expression : NAME'
try:
p[0] = names[p[1]]
except LookupError:
print "Undefined name '%s'" % p[1]
p[0] = 0
def p_error(p):
print "Syntax error at '%s'" % p.value
import ply.yacc as yacc
yacc.yacc()
while 1:
try:
s = raw_input('calc > ')
except EOFError:
break
if not s: continue
yacc.parse(unicode(s))
|
